This research will examine the extent to which chronic maintenance of animals on methadone interferes with operant behavior and will delineate the variables which controls this effect. The use of the precise laboratory techniques of operant psychology will provide a sensitive repertoire of baseline behaviors under experimental control which will allow study of the effects of methadone maintenance on performance. Our investigations will include determination of the effects of stimulus control variables on the behavioral actions of methadone in pigeons and rhesus monkeys, the effects of methadone on performance controlled by temporal stimuli, and the effects of schedule variables on the rate-altering effects of acute and repeated methadone administration. Finally, once these phenomena have been determined, the interactions of the effects of chronic methadone and those of acutely administered ethanol, amphetamine, pentobarbital, and tetrahydrocannabinol will be determined.